How to Grow Large Pumpkins
By Anna Graizbord
, last updated February 4, 2011
Pumpkins are great to have around in the fall for Halloween, Thanksgiving, and other harvest celebration-related activities, and everyone wants to grow the largest pumpkins. Whether you’re planning on making pumpkin pie, soup, muffins, or just want some festive jack-o-lanterns, larger pumpkins will likely do the job the best.
Growing Large Pumpkins From The Seed
A genetically strong seed will increase your chances of growing large pumpkins. For example, Howard Dill's patented Atlantic Giant has been a favored world champion seed in producing large pumpkins. If you’re looking to break records, this particular variety is the way to go. Otherwise Dill’s Prizewinner variety tops around 200 lbs.
- Plant anytime from May to June or any time you’ll get three to four months of warm growing days with above 75 degrees Fahrenheit during the daytime. Remember to plant after the threat of the last frost. Otherwise, you can start your seed indoors and transfer outside once soil reaches above 55 degrees Fahrenheit.
- Spade soil about a foot deep and mix in compost, manure, or well-balanced fertilizer. The pH level of the soil should be between 6.5 and 6.8.
- If you are staring inside, plant the seeds with pointed end facing down in 6-inch peat pots. Ensure that the temperature of the soil between 85 and 90 degrees Fahrenheit. Most seeds will germinate within 5 days. Once the first leaves appear or when the roots begin to grow through the pot, usually seven to ten days after germination, transfer outdoors.
- If you’re starting directly outside, plant two or three seeds in a group about an inch apart in moist soil. Cover seeds with about one half-inch of soil, which you should also moisten and gently press firm. Then, sprinkle another half-inch of soil loosely on top.
- You may want to build a mini-greenhouse over the seedlings for to shield them from wind and frost for up to six weeks. To do so, simply nail two storm windows together to form a triangle or a 4' x 4' wooden structure. Once plants outgrow it, use a temporary fence.
- Keep the soil moist, but not wet. Too much water will slow plant growth and encourage fungus diseases. Give seedlings a fertilizer that is specially formulated for seedling growth. These fertilizers are higher in phosphorus content and may be labeled with the nutrient proportions "15-30-15." Once fruits are established, it is best to use a more balanced formula, which might be labeled "20-20-20."
- Eight to ten weeks after you see growth, the first female flowers will appear. They will have a small pumpkin at their base. For best results, hand-pollinate the flowers every morning by locating a freshly-opened male flower, removing the outer flower petals, and gently swabbing the internal parts of a female flower with the male flower.
- Once a pumpkin has set, its position on the vine is crucial. If your pumpkins are not naturally at right angles to the vine, coax them gradually over about a week's time until it is.
- If you really want large pumpkins, you should apply a water-soluble plant food once or twice a week following the directions on the packaging.
Maintenance & Tips for Growing Large Pumpkins
- Setting a pumpkin as early as possible, preferably before early July, is important for growing large pumpkins. The earlier you set a pumpkin, the longer it has to grow until harvesting.
- Prune main vines early in the season when they have reached 10' to 12' beyond a set fruit. With vines 10' beyond the main root, cut the end of that vine once it is 20' to 24' long. Do not allow side shoots to grow longer than 8' before you cut off tips. Bury the ends of cut vines to reduce water loss.
- In late July, use a fertilizer formula that is high in potassium, which is around 15-11-29 in nutrient proportions. Be aware that too much fertilizer can be more damaging than helpful.
- Measure your pumpkins at least weekly. Adding together the circumference and height measurements and multiplying by 1.9 will give you an estimate of the pumpkin's weight.
- Choose the pumpkin that is growing the fastest. Generally, young pumpkins that are round and full grow the largest.